I would think hostname is a pretty hefty operation for genarating a session id, I'm not sure but I think it does a DNS lookup.

The ID is based on hostname, time, and some psuedo-random data. I've run a test with this to generate 50,000 IDs as fast as possible and check for collisions -- I didn't get any.

I use this for session ids (which I took from one of the Apache::Session modules) 

use Digest::MD5;
$session_id = substr(md5_hex(md5_hex(time() . {} . rand() . $$)), 0, 3
+2);

[download]
I ran it within the same process over 100,000 times with no collisions.

This is sort of slow, but strong. Reducing the param for rand() will speed things, but make collisions more likely.

I am no crypto expert, but from what I know, Its not really any stronger than if you didn't do it this way. Using MD5 and different text each time, it is highly unlikely that you will find a collision actually, that is just the nature of MD5 and hashing algorithms in general.

-stvn

In reply to Re: MD5-based Unique Session ID Generator by stvn
in thread MD5-based Unique Session ID Generator by radiantmatrix

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